Roles of O-linked oligosaccharides in immune responses

Many functional glycoproteins are expressed on the lymphocyte cell surface. Some of them carry O-linked oligosaccharides (O-glycans), which are conjug ated through serine or threonine residues. During Various biological proces ses, including T-cell activation, a tetrasaccharide on the T-cell surface i s dramatically converted to a branched hexasaccharide, called core2 O-glyca n, The same structural change in O-glycans is also found on the lymphocytes from patients with immunodeficiency conditions such as Wiskott-Aldrich syn drome and AIDS. Several studies revealing the roles of core2 O-glycans in i mmune responses show that this is a biologically significant change. In par ticular, core2 O-glycans expressed on the cell surface reduce cell-cell int eractions, thereby regulating immune responses, Furthermore, core2 O-glycan is a key backbone structure in forming selectin ligands, Thus, O-linked ol igosaccharides, in particular those containing core2 branches, play vital r oles in immune responses and may play dual roles in certain situations. Thi s review will summarize the results obtained from various studies investiga ting the roles of O-glycans in immunological processes, (C) 2001 John Wiley & Sons, Inc.